Method and apparatus for igniting and burning gaseous fuel



1965 D. M. MARSHALL ETAL 3,202,200

METHOD AND APPARATUS FOR IGNITING AND BURNING GASEOUS FUEL Filed Oct.27. 1960 2 Sheets-Sheet 1 FIG.1

15 INVENTORS David M. Marshall BY Andrew B. Sreever ATTORNEY 24, 1965 D.M. MARSHALL ETAL 3,202,200

METHOD AND APPARATUS FOR IGNITING AND BURNING GASEOUS FUEL Filed Oct.27. 1960 2 Sheets-Sheet 2 IIIII a A U IIIIII IIHIII IN V EN TORS DavidM. Marshall Andrew B. Sfeever AT TORNEY- United States Patent 3,202,200METHGD AND APPARATUS FGR IGNITING AND BURNENG GASIEQUS FUEL David M.Marshall, Akron, Ghio, and Andrew B. Stecver, Old Greenwich, Conn.,assignors to The Bab'cock & Wilcox Company, New York, N.Y., acorporation of New Jersey 1 Filed Get. 27, 1960, Ser. No. 65,447

8 Claims. (Cl. 158-109) The present invention relates to the combustionof fuel, and more particularly to a liquid cooled burner for hightemperature and high pressure service, and to a method of igniting andburning the fuel delivered by such aburner.

The use of liquid cooling in fuel burners has heretofore been known andvarious designs of such burners have proven reasonably satisfactory inlow pressure combustion service. However, when the space served by theburner has been operated at high pressures, such as 1000 p.s.i.a. andabove, the burner fluid cooling provisions have become unwieldy,complicated, and entirely unsatisfactory.

In the present invention, we provide a burner assembly suitable for highpressure and high temperature furnace operation. In such a burner, anovel method is provided for igniting the fuel supplied to the burnerand for maintaining stable combustion conditions within the furnace orcombustion space. The burner assembly includes an elongated nozzleconstructed from a plurality of small diameter pipes arranged inside-by-side spaced relation. The pipes are connected for the flow of acooling fluid therethrough and the nozzle assembly is provided withelongated slot-like openings between adjacent pipes for the discharge ofthe fuel from the burner nozzle. In a preferred form of the invention,space confining walls define an annular flow passageway for combustionair, for example around the nozzle. The combustion air is preferablyintroduced into the flow passageway with a tangential component ofmotion so that it will whirl in a generally helical flow path around aplurality of outlet slots adjacent the end of the nozzle.

When the burner is serving a furnace operated at super atmosphericpressures, of the order of 1000 p.s.i. and above, it is advantageous toreduce the number of openings in the furnace as much as possible so asto avoid unnecessary weakening of the furnace wall structure. Inaccordance with another aspect of our present invention, We providemeans for igniting the fuel delivered through the burner nozzle by meansof a spark ignition electrode positioned in the fluid flow path leadingto the burner nozzle. With such an arrangement, a low fuel pressurepilot flame is ignited and moves along the interior of the burner nozzleto discharge from the slotted nozzle outlet. The movement of the ignitedfuel is accomplished by the admission of additional fuel which pushesthe flame through the nozzle slots and into the furnace. The additionalfuel may be from either a high or low pressure source, and preferablythe former. As the flame leaves the nozzle outlets, it ignites the highpressure fuel stream discharging into the combustion air or high oxygencontent gases which are whirling through the combustion air passageway.This novel means for igniting and burning either high or low pressurefuel in the same burner assembly minimizes the number of openings in thewalls of the furnace and has moreover, proven entirely reliable forigniting and maintaining the combustion of fuel under pressurized hightemperature combustion conditions.

The various features of novelty which characterize our invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its 3,202,200Patented Aug. 24, 1965 use, reference should be had to the accompanyingdrawings and descriptive matter in which we have illustrated anddescribed a preferred embodiment of the invention.

Of the drawings:

FIG. 1 illustrates a high pressure, high temperature regenerative heaterprovided with the burner of the present invention;

FIG. 2 is an enlarged elevation, in section, of the burner assembly; and

FIG. 3 is a further enlarged section of the burner nozzle taken on line3-3 of FIG. 2.

The fuel burner of the present invention is illustrated as applied insupplying fuel to a high pressure, high ternperature regenerative heater10 where the hot gases produced by combustion in the upper portion ofthe heater give up heat to a bed of heat exchange pellets or pebblesmaintained in the lower and intermediate portions of the heater. Theflow of the hot combustion gases is down wardly from the upper portionto a gas discharge at the lower end portion of the heater. After theheat exchange bed has been heated to a desired value, the admission offuel and air ceases and a high pressure relatively cool gas isintroduced into the lower portion of the heater body for upward movementthrough and discharge into a side outlet from the upper portion of theheater. In passing through the heater, the high pressure, relativelycool gases are heated to a desired value for subsequent use.

In the heater illustrated, the heating and cooling of the heat exchangebed is cyclic, and in this particular embodiment of the invention, therelatively cool high pressure air is heated in the regenerative heaterfor discharge at a temperature of the order of 4000 F. and at a pressureof approximately 2000 p.s.i. To attain this heating effect, the burnerfirst must be operated in order to bring the heat exchange bed to thecomparable 4000 F. temperature and the fuel must be burned at a pressurehigh enough to insure passage of the heating gases through the heatexchange bed.

The regenerative heater 10 illustrated in the drawing forms the subjectmatter of a copending application Serial No. 831,994, filed August 6,1959, now Patent No. 3,120,380, in which a co-inventor is also aco-inventor of the present application. As disclosed and claimed in thesaid copending application, and shown generally in FIG. 1 of the presentapplication, the regenerative heater 10 includes an upright heavy walledpressure vessel 11 having integral upper and lower nozzles 12 and 13respectively, of reduced horizontal cross-sectional dimensions. Theupper nozzle 12 provides a confined space for the admission ofcombustion air and fuel, which is burned in that portion of the pressurevessel 11 above the upper surface of the bed of heat transfer pebblesdisposed therein. In a similar manner, the lower nozzle 13 is providedwith an outlet fitting 14 for the discharge of spent heating gases andan inlet fitting 15 for the introduction of the high pressure gas or airto be heated which is discharged through an outlet 19.

As shown in FIGS. 1 and 2, the upper nozzle 12 is cylindrical with itsaxis coaxial with that of the pressure vessel. The upper end of thenozzle is flanged as at 16 and is provided with a cover plate 17 whichis attached thereto. The plate is formed with a central opening 18through which the burner nozzle 20 of the burner assembly'extends. Acollar 21 mounted on the plate 17 sup ports a cap plate 22 to which iswelded (for example) a fuel inlet pipe 23 and cooling fluid inlet andoutlet chambers 24 and 25, respectively. The cap plate 22 is removablyattached to the collar 21 and the cover plate 17 by circumferentialseries of bolts 28, so that the assembly, including the burner nozzle20, may be removed for maintenance or replacement, as necessary.

The burner nozzle is formed from a plurality of U- shaped tubes 26, ashereinafter described in detail, with the opposite ends of each tubeopening to the inlet and outlet chambers 24 and 25, respectively, forthe flow of a cooling fluid, is. water, therethrough. The inlet andoutlet chambers are defined by a dome shaped hollow member 27 ofcircular horizontal cross-section in cooperation with the fuel inletpipe 23. The cylindrical wall portion of member 27 is welded to theupper surface of the plate 2 2. Suitable diaphragms (not shown) extendwithin the annular space between the member 27 and the exterior surfaceof the pipe 1-3 to separate the inlet and outlet chambers 24 and 25,respectively. The chambers are provided with flanged pipe connections 39and 31 for the admission and discharge, respectively, of the coolingfluid.

The burner nozzle 20 is constructed of a plurality of steel tubes 26arranged in spaced side-by-side relationship, as shown in FIGS. 2 and 3,to define a burner nozzle of generally circular cross-section. Each tubeof the nozzle assembly forms a complete flow circuit from the waterinlet chamber 24, through a return bend 32 at the lower extremity of thenozzle, to open into the fluid outlet chamber 25. The tubes 26, adjacentthe return bend portions 32, are swaged over a portion of their heightto form a plurality of axially elongated slots 33 between adjacenttubes.

In order to provide a gas-tight burner nozzle, the space between thetubes 26 is continuously welded, as at 26', with reinforcing and sealingwires 2-6 incorporated in the weldment as shown in FIG. 3. Thisconstruction prevails throughout the lengths of the extending nozzletubes 26 except in that region where the tubes are swaged to provide theslots 33 between adjacent tubes. Additionally, to effect a seal at theupper ends of the nozzle tubes, adjacent the lower annular plate of thehousing 29, the housing is welded to the plate 22 and the tubes 26 arewelded to the lower plate where they project through the housing 29.Thus, fuel gas passing downwardly through the fuel inlet pipe 23 intothe nozzle 20 is discharged from the nozzle in a plurality ofhorizontally directed jets.

In the embodiment shown, the slots 33 are each approximately 2% incheslong and 4 inch wide and the internal diameter of the nozzle 20 is 3inches. In the illustrated example, the exterior of the nozzle 20, withthe exception of the vertically elongated slotted openings,

is coated with a protective coating of Nichrome which is flame sprayedthereon. A refractory material 34 supported on the tubes 26 of thenozzle 20 by stainless steel rings 35, for example, is provided toreduce the heat absorption of the tubes 26.

With the described construction, the tubes 26 are each /3 inch 0D. witha wall thickness of .120", and advantageously have sufficient strengthto withstand an external pressure of 2000 p.s.i.a. without crushing. Asshown, the burner nozzle 2%) is covered in part by the refractorymaterial 34, such as zirconia, to reduce the heat absorption of thewater cooled tubes of the nozzle.

As disclosed in said copending application and shown in FIGS. 1 and 2,combustion air is introduced into the annular space 36 between the innerwall of nozzle 12 and the burner nozzle 29, entering through fourcircumferentially equally spaced tangential inlets 37. Thus, a whirl ingor rotary motion is imparted to the combustion air in its passingdownwardly through the nozzle 12 to enter the upper end portion of thepressure vessel 11. The

turbulence resulting from the whirling motion of the bustion air. Asshown schematically in FIG. 1, the air is supplied at 12 p.s.i.g., forexample, from an air compressor 49, with the air passing through aconnecting pipe 41 leading to the four tangentially arranged air inletopenings 37 in the wall of the nozzle 12. Oxygen may be admitted to thepipe 41 through a valved pipe connection 48. A separate low pressure airsource, provided from a fan 42, is connected by a pipe 43 with the pipe41 from the high pressure air compressor 40. The low pressure air systemis also connected through a separate pipe 44- with the natural gassupply pipe 45 whch leads to the nozzle 29, as hereinafter described.Both the high pressure air line 41 and the low pressure air line 43, 44are suitably provided with check valves, flow regulating and closurevalves generally indicated at 46.

Natural gas is provided at 15 p.s.i.g., for example, through a pipe 50which directly connects via line 45 with the gas inlet pipe 23 of theburner nozzle 29 In addition, a separate low pressure gas line 51connects with the pipe 50 for the delivery of 3 p.s.i.g., for example,gas to the burner nozzle 20, when required. The low pressure gas line isprovided with a flow regulating valve 52 which is actuated by a pressureswitch 53 actuated by the pressure in the gas line 45. The pressureswitch may be adjusted to close the low pressure valve 52 at an increasein pipe pressure to, for example, 4 p.s.i.g. Between the low pressuregas pipe 51 connection with the pipe 45, and the burner nozzle 26, ispositioned a gas bypass pipe 54 where the pipe 45 and the bypass pipe 54are provided with a pressure control valve 55 and a flow control valve56, respectively.

In accordance with the present invention, a spark plug 57 is inserted inthe gas pipe 45 ahead of the burner nozzle 20 and after the connectionbetween the bypass pipe 54 and pipe 45. The arrangement is such thateither low pressure gas with low pressure air or high pressure gas maybe delivered to the burner nozzle 29 While either low pressure air orhigh pressure air, enriched with oxygen, as desired, may be delivered tothe combustion air space 36 surrounding the burner nozzle 20.

When starting up the burner, it is customary to introduce low pressureair through the connecting pipe 44 and pipes 45 and 23, thence into theburner nozzle 2%, so as to purge the system. To operate the burner, thelow pressure gas is passed sequentially through pipes 51, 45, 54 and 45and simultaneously the spark plug 57 is actuated. When the gas reachesthe spark plug, it is mixed with low pressure air present as a result ofthe purging operation and low pressure air which is introducedsimultaneously with the low pressure gas, where the mixture is ignited.The flame progresses through the burner pipe 23 then enters into and isdischarged from the burner nozzle 20 through the slots 33. Immediatelythereafter the high pressure gas valves are opened while simultaneouslyboth the low pressure air flow and the low pressure gas flow arediscontinued. The high pressure gas, in passing through the pipe 45,closes the valve 52 and continuing its flow pushes the burning mixtureof air and low pressure gas through the nozzle 20 with the flameinitiated by the low pressure gas igniting the high pressure gas as thelatter leaves the nozzle 26 through the slots 33 to establish normalhigh pressure fuel combustion conditions. It is, of course, understoodthat opening the high pressure gas line necessitates the use of highpressure air so that the flame may then be stabilized with the properquantities of gas and oxygen. It has been found possible to initiateflow of high pressure air through the ports 37 before the high pressuregas is introduced, without aflecting the ignition of the low pressuregas and air.

In the normal cyclic operation of the heat transfer apparatusillustrated, the combustion of the gaseous fuel occurs for a limitedperiod of time, usually some fraction of an hour. Thereafter, with fuelcombustion stopped, the air or gas to be heated is introduced into J theheat transfer apparatus through inlet 15, passing upward through the bedfor another fraction of an hour, with the firing cycle thereafterrepeated.

It will be noted the present invention provides a fuel burner adaptedforuse as an igniter as well as a main burner, and constructed andarranged for cyclic operation where the fuel burning portion of thecycle is conducted at relatively low pressures and the burner is capableof withstanding extremely high pressures and temperatures during its offperiod. During the high pressure portion of the cycle, the high pressuremedium enters the burner nozzle so that both the exterior and interiorportions of the burner nozzle are exposed to the pressure andtemperature effects of the medium, and thus equalizes the effect ofpressure on the nozzle. Advantageously, the burner nozzle is fluidcooled so as to minimize the adverse influence of the high temperaturemedium on the burner nozzle.

While in accordance with the provisions of the statutes we haveillustrated and described herein the best form and mode of operation ofthe invention now known to us, those skilled in the art will understandthat changes may be made in the form of the apparatus disclosed withoutdeparting from the spirit of the invention covered by our claims, andthat certain features of our invention may sometimes be used toadvantage without a corresponding use of other features.

What is claimed is:

1. A burner nozzle comprising an elongated tube having a closed end anda plurality of discharge openings spaced around the periphery of andadjacent said closed end, said elongated tube being defined by aplurality of spaced hollow tubular members positioned with their axessubstantially parallel to the longitudinal axis of said elongated tube,the intertube spaces being closed on opposite ends of said dischargeopenings, each of said tubular members being directly and solely flowconnected at the closed end of said elongated tube with another saidtubular member to cool the closed end of said burner nozzle, and meansfor passing a fiuent cooling medium through said tubular members.

2. A fuel burner comprising an elongated tube having a closed end and aplurality of elongated discharge openings spaced around the periphery ofand adjacent said closed end, means for cooling said elongated tubeincluding a plurality of return bend tubes connected in gas tightrelationship to define the wall and closed end of said elongated tube,means for passing a fuel constituent through said elongated tube fordischarge through said discharge openings in an outward direction fromthe closed end portion of said tube, wall means spaced from the wall ofsaid elongated tube and defining a combustion air flow passagewaysurrounding said elongated tube, and means for passing combustion airthrough said passageway in mixing relationship with the fuel constituentdischarged through the openings of said elongated tubev 3. A fuel burnercomprising an elongated nozzle of circular crosssection having a closedend, a plurality of tubular members defining the wall and closed end ofsaid nozzle, each of said tubular members being bent across the closedend of said nozzle, means for passing a cooling medium through saidmembers, means for passing fluent fuel through said nozzle, meansadjacent an end of said nozzle for directing the fuel dischargedtherefrom transversely of the longitudinal axis of said nozzle, wallmeans spaced from and substantially parallel to the exterior surface ofsaid nozzle to define a combustion air passageway therebetween, saidwall means diverging away from said nozzle in the vicinity of the fueldischarge position of the nozzle, means for introducing combustion airinto said passageway upstream of the fuel discharged from said nozzle,said combustion air moving axially of said nozzle with a transversedirection of swirling motion imparted thereto for intimate mixing ofsaid fuel and combustion air leaving said fuel burner.

4. A fuel burner comprising an elongated nozzle of circularcross-section having a closed end, a plurality of U tubes arranged incircumferentially spaced side-byside relationship to define the wallsand end of said nozzle, means for passing a cooling medium through saidU tubes, means for passing fluent fuel through said nozzle, meansadjacent the closed end of said nozzle for directing the fuel dischargedtherefrom transversely of the longitudinal axis of said nozzle, wallmeans spaced from andsubstantially parallel to the exterior surface ofsaid nozzle to define a combustion air pa-ssageawy therebetween, saidwall means diverging away from said nozzle in the vicinity of the fueldischarge position of the nozzle, means for introducing combustion airinto said passageway upstream of the fuel discharged from said nozzle,said combustion air moving axially of said nozzle with a transversedirection of swirling motion imparted there-to for intimate mixing ofsaid fuel and combustion air leaving said fuel burner.

5. In a fuel burner the combination comprising an elongated nozzlehaving an opening in an end thereof, means for directing a flow of highpressure combustion air externally past said nozzle, a gaseous fuelsupply pipe connected to and discharging fuel into said nozzle, anignilter positioned in said supply pipe upstream of said nozzle, asource of high pressure gaseous fuel and a source of relatively lowpressure gaseous fuel, valved means separately connecting said sourcesof fuel with said fuel supply pipe, and valved means for connecting asuperatmospheric low pressure source of air with said supply pipe forintroduction of air to said elongated nozzle.

6. In a fuel burner having an elongated nozzle with a plurality ofdischarge openings in an end thereof for discharge of fuel substantiallytransverse to the axis of said nozzle, means for directing a flow ofhigh pressure combustion air externally past the discharge openings ofsaid nozzle, a gaseous fuel supply pipe connected .to and dischargingfuel into said nozzle, an igniter positioned in said supply pipeupstream of said nozzle, a source of high pressure gaseous fuel and asource of relatively low pressure gaseous fuel, valved means sepa ratelyconnecting said sources of fuel with said supply pipe, and valved meansfor connecting a low positive pressure source of air with said supplypipe for selective introduction of air to said elongated nozzle.

7. -In a fuel burner having an elongated fluid cooled nozzle with aplurality of discharge openings in an end thereof for discharge of fuelin directions substantially transverse .to the axis of said nozzle,means for directmg a whirling flow of high pressure combustion airexternally past the discharge opening of said nozzle, a gaseous fuelsupply pipe connected to and discharging fuel into said nozzle, anigniter positioned in said supply pipe upstream of said nozzle, a sourceof high pressure gaseous fuel and a source of relatively low pressuregaseous fuel, valved means separately connecting said sources of fuelwith said supply pipe for selected flow of gaseous fuel to said supplypipe, and valved means for connecting a low positive pressure source ofair with said supply pipe for introduction of air to said elongatednozzle.

8. In a fuel burner having an elongated fluid cooled nozzle surroundedby a confined combustion air flow passageway, the method of operatingsaid burner which comprises the steps of passing a stream of lowpressure air through said nozzle, introducing a flow of low pressuregaseous fuel into said nozzle, igniting the mixture of air and gaseousfuel in said nozzle and passing the burning mixture from said nozzleinto said confined combustion air flow passageway, introducing aseparate stream of high pressure gaseous fuel into said nozzle whilesimultaneously stoping flow of said air and said low pressure gaseousfuel to said nozzle, and passing a whirling stream of high pressurecombustion air through said confined combustion air flow passageway tosustain the combustion :of the high pressure gaseous fuel dischargingfrom said nozzle and ignited by the low pressure burning mixture ignitedin said nozzle.

References Cited by the Examiner UNITED STATES PATENTS Reiohhelrn 158-99Fischer 158-119 X Danforth 158-1175 Lilge 158-109 Forster 158-118 Alfery236-1 Witzke 122-235 Nagel 158-1175 Patterson 158-99 Furczyk v 158-7 XPeters 158-115 OCathey et a1. 158-109 Wright 158-115 FOREIGN PATENTSGreat Britain.

JAMES W. WESTHAVER, Primary Examiner.

FREDERICK KETTERER, FREDERICK L.

MATTESON, JR., Examiners.

2. A FUEL BURNER COMPRISING AN ELONGATED TUBE HAVING A CLOSED END AND APLURALITY OF ELONGATED DISCHARGE OPENINGS SPACED AROUND THE PERIPHERY OFAND ADJACENT SAID CLOSED END, MEANS FOR COOLING SAID ELONGATED TUBEINCLUDING A PLURALITY OF RETURN BEND TUBES CONNECTED IN GAS TIGHT RELATIONSHIP TO DEFINE THE WALL AND CLOSED END OF SAID ELONGATED TUBE,MEANS FOR PASSING A FUEL CONSTITUENT THROUGH SAID ELONGATED TUBE FORDISCHARGE THROUGH SAID DISCHARGE OPENINGS IN AN OUTWARD DIRECTION FROMTHE CLOSED END PORTION OF SAID TUBE, WALL MEANS SPACED FROM THE WALL OFSAID ELONGATED TUBE AND DEFINING A COMBUS-